bool GENERIC_LOOP_ALGO()

in src/h3lib/include/polygonAlgos.h [67:126]

• 36 lines of code
• 8 McCabe index (conditional complexity)

bool GENERIC_LOOP_ALGO(pointInside)(const TYPE* loop, const BBox* bbox,
                                    const GeoCoord* coord) {
    // fail fast if we're outside the bounding box
    if (!bboxContains(bbox, coord)) {
        return false;
    }
    bool isTransmeridian = bboxIsTransmeridian(bbox);
    bool contains = false;

    double lat = coord->lat;
    double lng = NORMALIZE_LON(coord->lon, isTransmeridian);

    GeoCoord a;
    GeoCoord b;

    INIT_ITERATION;

    while (true) {
        ITERATE(loop, a, b);

        // Ray casting algo requires the second point to always be higher
        // than the first, so swap if needed
        if (a.lat > b.lat) {
            GeoCoord tmp = a;
            a = b;
            b = tmp;
        }

        // If we're totally above or below the latitude ranges, the test
        // ray cannot intersect the line segment, so let's move on
        if (lat < a.lat || lat > b.lat) {
            continue;
        }

        double aLng = NORMALIZE_LON(a.lon, isTransmeridian);
        double bLng = NORMALIZE_LON(b.lon, isTransmeridian);

        // Rays are cast in the longitudinal direction, in case a point
        // exactly matches, to decide tiebreakers, bias westerly
        if (aLng == lng || bLng == lng) {
            lng -= DBL_EPSILON;
        }

        // For the latitude of the point, compute the longitude of the
        // point that lies on the line segment defined by a and b
        // This is done by computing the percent above a the lat is,
        // and traversing the same percent in the longitudinal direction
        // of a to b
        double ratio = (lat - a.lat) / (b.lat - a.lat);
        double testLng =
            NORMALIZE_LON(aLng + (bLng - aLng) * ratio, isTransmeridian);

        // Intersection of the ray
        if (testLng > lng) {
            contains = !contains;
        }
    }

    return contains;
}